This short English grammar test will tell you if you're level A, B or C on the CEFR scale for receptive English skills (listening and reading). Although I didn't build it, I haven't found a more accurate English grammar test anywhere, at least not for free. There's a longer version of this same English grammar test that gives you a more precise score and you can publish that score straight to your LinkedIn profile if you want to. If you're really looking for a challenge, there's a 2 hour version which tells you what you'd score on the TOEFL and IELTS if you took those tests. All three English grammar tests are available at no charge over on the site of the test's makers.
When you're looking for an English grammar test, it's better to choose a test that evaluates English grammar usage, that is to say, English in context, rather than just testing rules. Memorizing English grammar rules and being able to recite them on command doesn't necessarily lead to mastery of English. That's what I like so much about this particular suite of English grammar tests, as compared to others I've tried. They test English in context, making sure you can use grammar rules, while also checking that you have enough vocabulary to understand everyday English. Free is also nice.